1. Field of the Invention
The present invention relates to a method for modifying a polymer, more specifically relates to a method for reacting a compound having a nitroxide radical in the molecule thereof and a radical initiator to a polymer capable of decomposing with a carbon radical in the molecule thereof to thereby decrease the molecular weight of the polymer and to also introduce a functional group into the polymer.
2. Description of the Related Art
For example, as described in Japanese Patent Publication (A) No. 10-182881, it has been proposed to compound stable free radicals such as TEMPO (i.e., 2,2,6,6-tetramethyl-1-piperidinyloxy radicals) into rubber to improve the physical properties of the rubber composition, in particular the physical properties such as processability and abrasion resistance. Further, Japanese Patent Publication (A) No. 8-239510 discloses to introduce a TEMPO derivative into a polymer to prevent aging of the polymer. However, there is no technology relating to the modification of the polymers by the intentional formation of a carbon radical in polymers such as rubber using a compound having stable free radicals in its molecule. The technique of using a nitroxide radical for modifying a polymer is described in U.S. Pat. No. 4,581,429, but this introduces the nitroxide radicals as a counter radical for living radical polymerization and is not used for the purpose of imparting functional groups. Japanese Patent Publication (A) No. 2003-524037 discloses a reaction in the presence of a free radical using a polyfunctional nitroxide radical as a reversible cross-linking agent, but this is not used for the purpose of imparting a functional group. U.S. Pat. No. 6,177,519 describes technology for decreasing the molecular weight of an isobutylene-p-methylstyrene copolymer, while grafting a vinyl silane compound to use as a sealant or binder. However, there would be a high possibility of problems such that homopolymer of the vinyl silane compound is formed in the system. Note that the present inventors previously proposed the technique of using a nitroxide radical compound and a radical initiator to suppress the reduction in the molecular weight of a polymer, while introducing a functional group into the polymer (see Japanese Patent Application No. 2004-311135).
Since butyl rubber, EPM, etc. are low in polarity, the compatibility thereof with resins such as polyamides, polyesters and are inferior in bonding with glass etc. Therefore, to increase the polarity of these polymers and facilitate reaction at the interfaces, attempts have been made to use radical initiators to graft functional monomers. However, the constituent units of these polymers include units to be decomposed by hydrogen abstraction of the radicals, and therefore there is a very high possibility of a decrease in the molecular weight during the modification and also the radical initiator and a functional monomer are directly reacted to result in a decrease in the graft efficiency, the homopolymers, in some cases, are formed in the system. However, the decrease in the molecular weight increases the fluidity and tackiness of a polymer, so that property can be utilized as a binder, sealant, etc.
Accordingly, an object of the present invention is to develop a technique for introducing a functional group into a radical degradation type polymer, while intentionally decreasing the molecular weight.
In accordance with the present invention, there is provided a method for modifying a polymer comprising:
modifying a polymer capable of decomposing with a carbon radical in the molecules thereof by a reaction with a radical initiator and a compound having a nitroxide radical in the molecule thereof to decrease the molecular weight of the polymer and also to introduce an organic group derived from the free radical into the polymer and a modified polymer obtained from the same and a rubber composition containing the same.
According to the present invention, by reacting a radical initiator and a compound having a nitroxide radical in the molecule thereof to a polymer capable of decomposing with a carbon radical in the molecules thereof, it is possible to decrease the molecular weight of the polymer and also to introduce an organic group derived from the free radical into the polymer. It is preferable reaction with a ratio of the nitroxide radical/the radical initiator (molar ratio) of less than 0.7 is preferable.